Composite wood product, methods for manufacturing the same and methods for determining organic biocide concentration in a composite wood product

ABSTRACT

A composite wood product and methods for manufacturing the same and determining the concentration and distribution of an organic biocide within a composite wood product are provided. The organic biocide may be added to wood elements (i.e., fibers, flakes, strands, veneers) prior to consolidation and/or heating of the wood particles to form the composite wood product. A tracer additive may be mixed with the biocide, or applied separately to the furnish which is used to produce the composite wood product. The tracer additive may be detected via, for example, x-ray fluorescence. An amount of tracer additive detected may correlate to an amount of organic biocide within the wood elements and/or the composite wood product.

FIELD OF THE INVENTION

This invention relates generally to a composite wood product and methodsfor manufacturing composite wood products and determining aconcentration of an organic biocide within a composite wood product. Atracer element may be added to the organic biocide prior to compositewood product formation. The tracer element may be detected via, forexample, x-ray fluorescence spectroscopy. The amount of tracer elementdetected can be correlated to the amount of organic biocide within thecomposite wood product.

BACKGROUND OF THE INVENTION

Composite wood products are made from elements or particles of wood,commonly called furnish, which are consolidated and bonded together withadhesive resin(s). It should be understood that, in the presentapplication, the terms “element”, “particle” and “furnish” may be usedinterchangeably and may refer to any type of element from which acomposite wood product may be manufactured. It should further beunderstood that wood composites, as defined in this specification, referto those products which maintain the main properties of wood. Woodelements may include, for example, wood flour, fiber, fiber bundles,flakes, chips, wafers, strands, veneers, or combinations of the like.Different grades and/or types of composite wood products can bemanufactured depending on, for example, the wood species, size of thewood elements, and processing conditions. The elements are dried to themoisture content level required by the process. Then adhesive, biocides,and other types of additives such as, for example, waxes, are applied tothe furnish. This process may occur at one of many stages ofmanufacture, but commonly would occur during a process referred to asblending. Usually the blended furnish is then formed into a mat, whichis then consolidated under heat and pressure to form the final compositewood product.

Certain biocides can be applied to the furnish to impart decay and/orinsect resistance in the final product. Biocides typically used inindustrial applications include, for example, inorganic compounds, suchas zinc borate, sodium borate, or copper-containing salts. Many types ofinorganic compounds may be used as single preservatives, or may be usedin combination with other compounds as co-biocides to treat woodfragments prior to formation of a composite wood product.

Controlling biocide additive content may be critical to ensure properconcentration and distribution of active ingredients in the product.Uniform biocide distribution across the product enables economical andproper product protection against insects and fungi, including decay.Non-uniform concentration or distribution may lead to partial damage ofthe product by fungi or insects. Uniformity of biocide distributiondepends on the method of application. During application, a variety ofaccidental factors may appear which may result in non-uniformdistribution of biocides or application of biocides in quantitiesoutside the target range. Examples of some problems include clogging ofa spray nozzle with dust, contamination in biocide dispersion, a faultydispensing system, etc. In a production setting, such as a commercialsetting, it is difficult to quantify uniformity of treatment simply fromthe appearance of the blended wood furnish or in the final compositewood product. As a result, special analytical methods must be applied tothe product to identify active ingredient concentration anddistribution.

It has been found that wood preservatives containing certain elements,for example, chlorine, zinc and/or copper and/or chromium and/orarsenic, could be analyzed relatively quickly without special samplepreparation via x-ray fluorescence spectroscopy (“XRF”). This wasparticularly the case if such elements were introduced into the woodproduct in sufficient concentration (above 1000 ppm, but in some casesas low as 30 ppm). XRF analysis allows for the non-destructive analysisof a wide range of elements, typically those heavier than Fluorine (F).The basic principle behind XRF spectroscopy is the use of an energysource to excite an inner shell electron of an atom. Energy is appliedfrom a source, for example an appropriate radioisotope, under which theatom will emit an x-ray photon (fluoresce). If the applied energy is ofsufficient strength, an electron will be ejected from an inner ring.This electron will be replaced by an electron from an outer ring inorder to stabilize the atom. The movement of an electron to stabilizethe atom will emit an x-ray photon, which is counted by the detector.

It was also found that preservatives containing organic compounds suchas deltamethrin, chlorpyrifos or isothiazolone require a targetapplication level onto a wood product often as low as 10 ppm to 2000ppm. However, elements sensitive to XRF analysis are not present orpresent in less than sufficient concentrations to enable quick accurateanalysis of these products. Products treated with organic biocidesrequire complex sample preparation and sophisticated analytical methods,such as, for example, High Performance Liquid Chromatography (HPLC), GasChromatography (GC), or Neutron Activation Analysis (NAA). Even inisolated cases where sample preparation is not a major issue, thesemethods require specialized and expensive equipment, as well as trainedpersonnel. Neither is readily available or practical in a composite woodmanufacturing facility. The delay associated with such sophisticatedanalytical methods can be a major problem because it potentially allowsfaulty product to be manufactured without timely detection of defects. Aneed, therefore, exists for a method of determining a concentration anddistribution of a biocide within a composite wood product which is moreconvenient than known methods.

SUMMARY OF THE INVENTION

The present invention generally relates to wood composite manufactureand methods for indirectly quantifying the concentration anddistribution of an organic biocide within a composite wood product. Atracer element, or additive, may be added to the biocide. The resultantmixture may be applied to wood elements prior to composite wood productformation. The tracer element may be detected via, for example, x-rayfluorescence spectroscopy. An amount of tracer element detected can becorrelated to the amount of organic biocide within the composite woodproduct.

It was found that in composite wood products, organic biocidesfrequently cannot be detected in target application quantities inextracts prepared from the final composite products using known reliablewet chemistry methods. This may likely be a result, for example, ofpartial decomposition and/or fixation in the glue line. Adhesive resinsused in wood composites, such as, for example, phenolics, p-MDI,melamine or urea which become highly crosslinked, may be a significantfactor in an active's fixation. Such depletion of organic biocides maybe directly related to the product formation, type of adhesive usedand/or process conditions. However, according to the present invention,it has been found, unexpectedly, that the relationship between theassayed and target concentrations of tracer elements in composite andthe initial target concentration of additives of interest may beconnected through coefficients of retention, as will be described laterin more detail. This coefficient can be experimentally assessed andcalculated. Coefficient of retention is related to target and assayconcentrations of active ingredients and tracers as identified byanalytical methods in a composite wood product sample. Unexpected lossesof active ingredients during handling and/or the manufacturing processbecome visible from the unusually low level of tracer element detectedin the product, and knowledge of the coefficient of retention allowscalculation of the actual concentration of actives. The constant valueof a coefficient of retention within a relatively wide range ofconcentration of additive of interest as discovered makes the analysisdescribed above relatively accurate.

The present invention may provide solutions and/or dispersions carryingorganic biocides which may be formulated with one or more tracerelements that are suitable for XRF analysis. The quantities may be thoserequired for fast and/or accurate detection and may enable analysis ofconcentration and/or distribution of active ingredient in the compositewood product. To obtain uniform distribution at the ppm level, in anembodiment, biocides may be applied to wood fragments in the form ofdiluted solutions or dispersions, in concentrations of 0.001 to 10%.These concentrations may vary depending on the type of composite woodproduct, solution and/or dispersion design and/or other conditions ofmanufacture.

The tracer or additive may be mixed with the biocide prior toapplication to the wood furnish elements. The tracers implemented withinthe solutions and/or dispersions may be, for example, part of asynergistic biocide formulation. An example of such a tracer may be, forexample, zinc in zinc borate. It was found that biocides containingmetal or other elements sensitive to XRF analysis, such as, for example,zinc borate, could be prepared in a blend of powders, or in a dispersionin a common liquid carrier, such as water, which may also carry one ormore biocides. The use of a liquid dispersion of biocides has severaladvantages, such as, for example, lack of dust during handling; moreuniform distribution; and reduction of losses (dislocation) during thepressing process, particularly when steam injection is used. In someembodiments, an additional advantage may be that the formulation has asynergistic effect. For example, a combination of biocides may beapplied to the wood elements and may be monitored via one or more tracerelements. The combination may be more effective in protection ofcomposite wood products against insects or decay in comparison toindividual biocides.

Powder blends or liquid dispersions of the present invention may besprayed or applied onto wood elements before entering the blender, oronce inside the blender prior to consolidation into the composite woodproduct. It may be possible to apply tracer and organic biocideseparately into the blender using a connected system of multiple feederswith one feeder dedicated to tracer distribution and other(s) toadditive(s) of interest.

A first type of analysis may be performed on completed composite woodproduct samples. The products may be broken down and assayed for thepresence and distribution of active ingredients using the XRF technique.A second type of analysis may be conducted via installation of detectiondevices on or proximate to a manufacturing line, prior to compressionand/or heating of the elements to form the composite wood product. TheXRF technique may be applied for continuous monitoring of preservativedistribution on the production line. It could be performed before orafter the pressing operation. Stable preservatives containing metal, orother XRF sensitive elements, may be directly detected by XRF analysis.Concentration and distribution in wood composites of organic co-biocidesincapable of being directly detected, can be assessed indirectly basedon XRF analysis data with respect to the tracer concentration. This canbe achieved due to the coefficient of retention and relationship betweentracer assay and target values, as well as the known targetconcentration of an additive of interest. Assessment and calculation forthe coefficient of retention may be established in independentexperiments prior to commercial testing.

The coefficient of organic biocide retention “K” can be calculated fromthe following equation (1):K=(A ₂ ×Z ₁)/(A ₁ ×Z ₂)  (1)Where:

A₁=target concentration of biocide of interest in wood product

A₂=assayed concentration of biocide of interest in wood product

Z₁=target concentration of tracer element as applied to composite woodproduct

Z₂=assayed concentration of tracer element in wood product

The data required for calculation of this coefficient may be collectedfrom independent samples of formed composite wood products. The numberof samples evaluated for this purpose may depend on the requiredaccuracy of analysis for treated product, and the variability of theanalytical method used. Accordingly, when analytical data for thecalculation of coefficient of retention K is more consistent, fewersamples may require evaluation for calculation of coefficient ofretention. The calculated average from this experiment may be used inassessment of biocide concentration in samples of interest.

Based on the above-mentioned coefficient of retention, the concentrationof the biocide of interest in the sample can be calculated from equation2 or from a specially prepared calibration curve:A _(x)=(K×Z _(2x) ×A _(1x))/Z _(1x)  (2)Where:

A_(1x)=target concentration of biocide of interest in wood product

Z_(1x)=target concentration of tracer element in sample

Z_(2x)=assay of tracer element

K=coefficient of retention (as described in equation 1)

It is, therefore, an advantage of the present invention to provide amethod for determining a concentration of an organic biocide within acomposite wood product wherein the method is more convenient and/oraccurate than known methods for determining organic biocideconcentrations.

Additional features and advantages of the present invention aredescribed in, and will be apparent from, the detailed description of thepresent embodiments and from the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The embodiments of the present invention are described in detail belowwith reference to the following drawing.

FIG. 1 is a flowchart of a method of determining a concentration of abiocide in an embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to composite wood product manufacture andmethods for determining a concentration of an organic biocide within acomposite wood product. A tracer element may be added to the organicbiocide prior to composite wood product formation. In this regard, theorganic biocide and tracer may be added to wood elements (e.g., fibers,fiber bundles, flakes, strands, veneers) prior to consolidation of thecomposite wood product. It should be understood that use of the words“element”, “fragment” or “particle” references any type of wood furnishfrom which a composite wood product is manufactured. It should befurther understood that the term “composite wood product” may refer toany type of engineered wood product, such as, for example, mediumdensity fiberboard (MDF), particleboard, oriented strand board (OSB),waferboard, laminated strand lumber (LSL), plywood, laminated veneerlumber (LVL), parallel strand lumber (PSL), crushed long-fiber lumber(scrimber) or combinations of the like. The tracer element may bedetected via, for example, x-ray fluorescence spectroscopy. An amount oftracer element detected may correlate to an amount of organic biocidewithin the composite wood product.

The organic biocide may be, for example, a synthetic pyrethroid (e.g.permethrin, deltamethrin or bifenthrin), a triazole (e.g. tebuconazole,propiconazole), a nicotinoid (e.g. imidacloprid), a fiprole (e.g.fipronil) or the like. The additive may contain, for example, zinc,copper, nickel, cobalt, or any other element which may be detected viax-ray fluorescence and has an atomic weight greater than or equal to 10.FIG. 1 illustrates a flowchart of a method 100 for determining a biocideconcentration within a composite wood product in an embodiment of thepresent invention. In a first step, 102, the organic biocide andadditive, or tracer element, may be mixed together. This mixture mayoccur in, for example, a powder blend, dispersion, or other mediumsuitable for application onto the wood particles comprising the furnish.In other embodiments, the biocide and additive may be applied separatelyto the furnish, such as from differing streams in a blender systemconnected to, for example, a common metering system. In a next step 104,the biocide and the additive may be applied to wood furnish prior toconsolidation under heat and pressure.

Decision 106 represents a differentiation between two embodiments.Namely, in a first embodiment, the wood elements comprising the furnishare examined on, for example, a forming or assembly line, prior tocompression and/or heating to form the composite wood product. In asecond embodiment, analysis occurs after formation of the composite woodproduct. If the elements are to be examined on the forming line, anx-ray fluorescence system may be placed adjacent to the elements withinthe overall system for manufacturing an engineered composite woodproduct. An example of a suitable x-ray fluorescence equipment may be,for example, obtained from ASOMA® Instruments, Inc. The x-ray system maydetermine a quantity of additive in the wood product, as shown at step108. Based on this determination, a concentration and distribution ofbiocide in the composite wood sample may also be calculated, as shown atstep 110, using the equations previously outlined.

In an alternate embodiment, the elements comprising the furnish may becompressed and heated, as shown at step 112, after the biocide andadditive mixture is applied. Sufficient time may be allocated prior toobtaining the composite wood product sample, as shown at step 114. Thesample removed from the composite wood product may be, for example,ground for testing and may then be subject to x-ray fluorescence asshown at step 116. In another embodiment, a core portion of thecomposite wood product may be obtained for testing. It is assumed thatprevious testing of samples was conducted to determine a value for thecoefficient of organic biocide retention “K” in accordance with Equation1 mentioned above. The tracer concentration may be obtained as shown atstep 118. Knowing the target concentration of the biocide of interest,target concentration of tracer element, coefficient K and assay of atracer, the concentration of the biocide of interest in the sample canbe calculated from equation 2 as outlined above or identified from thecorresponding calibration curve. This step is illustrated at 120.

The invention and procedure of analysis may be described in thefollowing examples:

EXAMPLE 1

11.5 g of NATROSOL® 250 HB thickener, TAMOL® 681 (Rohm & Haas)dispersing aid and 11.5 g of BYK® 031 (BYK Chemie) defoamer were mixedwith 768 g of water using a high speed disperser. After dissolving thethickener, 2303 g of zinc borate (BOROGARD® ZB-US Borax) was added alongwith an additional 576 g of water and 11.5 g of IGEPAL® Co 630surfactant. When the dispersion became homogenous (with a Hegman grindof 6-7 as per ASTM D1210), an additional 192 g of water was added, alongwith 46 g of TIMBOR® (US Borax), 46 g of Versene (Dow Chemical), 156.7 gof DURSBAN® R (organic insecticide-Dow Agro) and 746 g of wax emulsion.Mixing was completed until a uniform dispersion was obtained. Productwas coded as a Preservative ZBDB.

EXAMPLE 2

2.8 g of KELZAN® (Xanthan gum-Kelco), 2.8 g of VAN GEL B® (Vanderbilt),3.8 g of TAMOL® 681 (Rohm & Haas) dispersing aid and 3.8 g of BYK® 031(BYK Chemie) defoamer were mixed with 509 g of water using a high speeddisperser. To the homogenous mixture, 1526 g of zinc borate (BOROGARD®ZB-US Borax) was added, together with 371 g of water and 7.6 g IGEPAL®Co 630. When the dispersion became homogenous, (a Hegman grind 6-7 asper ASTM D1210), an additional 7.5 g of water was added, together withTROYSAN® 174 (Troy) (10% in water). This was followed by TIMBERTREAT®DM-5 (Kop-Coat) in quantities shown in Table 1. Products were coded as aPreservatives ZBDM-1, ZBDM-3, and ZBDM-4. TABLE 1 Quantities ofTimbertreat and additional water used in formulation Timbertreat DM-5Water Formulations (g) (g) ZBDM-1 50 280 ZBDM-3 165 165 ZBDM-4 330 0

EXAMPLE 3

3.20 g KELZAN™ (Xanthan gum-Kelco), 7.38 g of TAMOL® 681 (Rohm & Haas)dispersing aid and 3.70 g of BYK® 031 (BYK Chemie) defoamer were mixedwith 492 g of water using a high speed disperser. To the homogenousmixture, 1477 g of zinc borate (BOROGARD® ZB-US Borax) was addedtogether with an additional 281 g of water and 7.36 g IGEPAL® Co 630.When the dispersion became homogenous, (approximately 6-7 a Hegman grindas per ASTM D1210), 9.8 g TROYSAN® 173 (Troy) (10% in water) in canpreservative was incorporated into the mixture, together with 239 g ofwax emulsion. An additional 97.5 g of TIMBERTREAT® DM-5 (Kop-Coat) wasthen added, and after thorough incorporation of active into thedispersion, the process was completed. The product was coded as aPreservative ZBDM-6.

EXAMPLE 4

120 lb. of dry aspen strands were loaded into a blender and sprayed withMDI adhesive for a period of 10 minutes. Resin content on the strandswas targeted at about 5%. This was followed by spraying of slack waxinto the blender as well as addition of the required quantity ofdispersion containing preservative made as described in examples 1, 2,and 3. Quantities of materials used are shown in Table 2. Three 2′×2′composite wood panels were made separately from each blender load usinga steam injection press according to standard industry procedure. TABLE2 Trial 1 Trial 2 Trial 3 Trial 4 Trial 5 Components lb. lb. lb. lb. lb.Wood Strands 200    110    110    110    120    MDI Adhesive 10   5.85.8 5.8 6   Preservative ZBDB 6.6 — — — — ZBDM-1 — 2.9 — — — ZBDM-3 — —2.9 — — ZBDM-4 — — — 2.8 — ZBDM-6 — — — — 2.6 Slack Wax 1.0  0.58  0.58 0.58 0.6

EXAMPLE 5

Five 2″×2″ specimens randomly selected from two out of three boards madeas described in Example 4 were used. The specimens were ground andassayed for zinc and organic biocide. Samples of products were ground toapproximately 30 mesh size and analyzed for zinc using a proceduredescribed in the American Wood Preservative Association Standard A9-01(XRF method). Organic biocides were analyzed by extraction from theindependent samples. Samples of ground wood approximately 4 g in weightwere Soxhlet extracted for 6 hours in cellulose thimblets using acetonewith 2% water. Extract was quantitatively transferred to 250 mlvolumetric flasks. 200 μl water was added to 800 μl extract. The samplewas mixed, then filtrated through a 0.45μ filter prior to HPLC analysis.

HPLC analysis was performed using a Hewlett-Packard HP 1100 HPLCimplementing a diode assay detector. UV signal at 230 nm was used tocalculate the reposted results. The analytical column used was a ZorbaxXDB-8 C8, 5 cm×4.6 mm id×3μ particle size. Flow rate was 0.75 ml/min.The results obtained from the analysis, and calculated coefficients ofretention of organic biocide, including the average K for trial 1 andthe combined average K for trials 2, 3, and 4, are shown in Table 3.TABLE 3 Calculation of coefficient of retention for organic biocidesused in treatment of wood products Target Assay Organic Zinc OrganicZinc Biocide Content Biocide Coefficient of Sample (Z₁) (A₁) (Z₂) (A₂)Retention Trial # ID ppm ppm ppm ppm (K) 1 4.2 1158 6000 1000 3630 388.64 1 2.5 1158 6000 1000 3465 375 .65 1 2.3 1158 6000 1000 3660 359 .591 6.10 1159 6000 1000 4120 365 .53 1 8.7 1159 6000 1000 3810 375 .59Average for trial 1 .60 2 3.7 1218 4551 11 3388 3.9 .48 2 8.7 1218 455111 3388 4.8 .59 2 1.1 1219 4551 11 3426 4.2 .51 2 6.1 1219 4551 11 33883.6 .44 3 6.1 1227 4698 38.1 3426 10.2 .37 3 10.1 1227 4698 38.1 334914.5 .53 3 3.7 1228 4698 38.1 3542 19.3 .67 3 8.7 1227 4698 38.1 308012.3 .49 4 1.1 1230 4385 73.1 3773 29.5 .47 4 10.1 1230 4385 73.1 317522.6 .43 4 6.1 1230 4385 73.1 3811 31.5 .50 4 8.7 1230 4385 73.1 358030.1 .50 4 6.1 1231 4385 73.1 2965 26.3 .53 Average for trials 2, 3, 4.50

EXAMPLE 6

The one remaining panel of the three manufactured from each furnishformulation as described in Example 4, (and not tested earlier forcoefficient of retention of organic biocides as described in Example 5),was used. The panels were cut into 2″×2″ samples. Two samples from eachpanel were analyzed for zinc content using XRF method and the proceduredescribed in Example 5. Based on these results, and the formulapresented earlier the concentration of organic biocide was calculatedusing equation 2. The results are shown in Table 4. TABLE 4 Theconcentration in wood products of organic biocides calculated based onzinc traces assay Assay Organic Organic Target Biocide Biocide OrganicZinc Concentration Concen- Zinc Biocide Assayed Calculated tration TrialSample (Z_(1x)) (A_(1x)) (Z_(2x)) (A_(x)) Assayed* # ID ppm ppm ppm ppmppm 1 6.4 1160 6000 1000 3965 396 418 6.5 1160 6000 1000 3965 396 408 21.1 1220 4551 11 3426 4.1 5.5 8.7 1220 4551 11 3580 4.3 4.4 3 6.1 12294698 38.1 3503 14.2 10.6 10.1 1229 4698 38.1 3157 12.8 10.1 4 6.1 12324385 73.1 3349 27.9 30.3 10.1 1232 4385 73.1 3349 27.9 26.0 5 13 15394379 38.6 3619 15.9 14.7 12 1543 4379 38.6 3426 15.1 16.7*Comparison data obtained from analysis of samples by extraction andHPLC technique.

After this evaluation, the remains of samples tested for zinc boratewere assayed for organic biocides using HPLC method as described inExample 5. The results were compared with those calculated in the lastcolumn of Table 4. The data evidences reasonable accuracy with respectto calculation of concentration of organic biocides based on one or moreassays of zinc traces and a determination of a coefficient of retentionvia experimentation. This also allows for qualification of distributionof biocide within the composite wood product. Data presented in Table 3also shows constant value of coefficient of retention, withinexperimental error, for tested biocides within the wide range ofconcentrations used. Small values (K<1) for coefficients of retentionsindicated a significant difference between target and assayedconcentrations of organic biocides observed during the making of woodcomposites.

While the embodiments of the invention have been illustrated anddescribed, as noted above, many changes can be made without departingfrom the spirit and scope of the invention. Accordingly, the scope ofthe invention is not limited by the disclosure of the embodiments.Instead, the invention should be determined entirely by reference to theclaims that follow.

1. A composite wood product comprising: a plurality of wood particles; aresin applied to the wood particles enabling adhesion between the woodparticles; a biocide applied to the wood particles; and an additiveapplied to the wood particles wherein the additive is detectable whenthe composite wood product is subject to an x-ray fluorescence analysisand wherein an amount of additive detected can be correlated to anamount of biocide within the composite wood product.
 2. The compositewood product of claim 1 being selected from a group consisting of:oriented strand board, laminated strand lumber, laminated veneer lumber,parallel strand lumber, plywood, particle board, fiber board and crushedlong-fiber lumber.
 3. The composite wood product of claim 1 wherein thebiocide is selected from a group consisting of: a synthetic pyrethroid,a triazole, a nicotinoid and a fiprole.
 4. The composite wood product ofclaim 1 wherein the additive contains an element having an atomic weightgreater than or equal to ten.
 5. The composite wood product of claim 1wherein the additive is selected from a group consisting of: zinc,barium and calcium.
 6. The composite wood product of claim 1 wherein thewood particles are selected from a group consisting of: flour, fibers,fiber bundles, flakes, chips, wafers, veneers and strands.
 7. A methodfor making a composite wood product comprising the steps of: providing aplurality of wood particles; applying a resin to the wood particlesenabling adhesion between the wood particles; applying a biocide and atracer additive to the wood particles wherein the tracer additive isdetectable when the composite wood product is subject to x-rayfluorescence spectroscopy and wherein an amount of tracer additivedetected can be correlated to an amount of biocide within the compositewood product; and heating and pressing the plurality of wood particlesto form the composite wood product.
 8. The method of claim 7 wherein thecomposite wood product is selected from a group consisting of: orientedstrand board, laminated strand lumber, laminated veneer lumber, parallelstrand lumber, plywood, particle board, fiber board and crushedlong-fiber lumber.
 9. The method of claim 7 wherein the biocide isselected from a group consisting of a synthetic pyrethroid, a triazole,a nicotinoid and a fiprole.
 10. The method of claim 7 wherein theadditive contains an element having an atomic weight greater than orequal to ten.
 11. A method for determining a concentration of an organicbiocide within a plurality of wood particles, the method comprising thesteps of: providing the plurality of wood particles; applying an organicbiocide to the plurality of wood particles; applying an additive to theplurality of wood particles wherein the additive is detectable when theplurality of wood particles is subject to an x-ray fluorescenceanalysis; subjecting the wood particles to an x-ray fluorescenceanalysis; measuring an amount of the additive detected within theplurality of wood particles; and correlating the amount of the additivedetected to an amount of the organic biocide within the plurality ofwood particles.
 12. The method of claim 1 wherein the additive containsan element having an atomic weight greater than or equal to ten.
 13. Themethod of claim 1 wherein the biocide is selected from a groupconsisting of: a synthetic pyrethroid, a triazole, a nicotinoid and afiprole.
 14. The method of claim 1 wherein the particles are selectedfrom a group consisting of: flour, fibers, fiber bundles, flakes, chips,wafers, veneers and strands.